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Sclerite calcification and reef-building in the fleshy octocoral genus Sinularia (Octocorallia: Alcyonacea)

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Abstract

Alcyonacean octocorals in tropical reefs are usually not considered as reef builders. Some Sinularia species, however, are capable of consolidating sclerites at the colony base to form spiculite. Nanwan Bay, southern Taiwan, features both fossilized and recently formed boulders composed of spiculite, thus demonstrating the role of Sinularia in contributing to the reef structure. Section radiography of an 18.5 kg spiculite boulder demonstrated a regular density banding of 3–6-mm intervals. Core survey indicated spiculite coverage of 25–30% on the live reef and of 30–40% on the uplifted boulders. Cores taken from living Sinularia revealed a distinct transition from discrete sclerites to compact spiculite and amorphous calcium carbonate cementing the sclerites. In the widespread S. gibberosa, sclerite formation appeared to start intracellularly, followed by a prolonged extracellular calcification process. At the calcification site, multiple sclerocytes formed expanded pseudopod-like membranes that interconnected, forming multicellular vesicles (MCVs) around the sclerites. The MCVs and the pseudopods disappeared at sclerite maturation, followed by degradation of the sclerocytes around the mature sclerites. At the colony base, granular vesicles were distributed among the sclerites, indicating a cementing process in progress. These findings suggest that colonies of Sinularia are able to cement sclerites and consolidate them at their base into spiculite, thus making them reef builders.

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Acknowledgments

The authors thank Mr. T.-S. Chen and the Administration of Kenting National Park, Taiwan for assistance with the fieldwork. Y. Benayahu was partly supported by the Israel Cohen Chair in Environmental Zoology. We also acknowledge the funding and electron microscope support from the Research Center for Biodiversity, Academia Sinica, Taiwan.

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Correspondence to M.-S. Jeng.

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Communicated by Geology Editor Prof. Bernhard Riegl

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Jeng, MS., Huang, HD., Dai, CF. et al. Sclerite calcification and reef-building in the fleshy octocoral genus Sinularia (Octocorallia: Alcyonacea). Coral Reefs 30, 925–933 (2011). https://doi.org/10.1007/s00338-011-0765-z

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